Aqueous phase oxidation process

ABSTRACT

An improved oxidization process may be used to oxidize a wide variety of feedstocks. Oxidation takes place in a reactor where the feedstock is mixed with an oxidizing acid, such as nitric acid. The reaction mixture may also include a secondary oxidizing acid such as sulfuric acid as well as water and/or dissolved and mechanically mixed oxygen gas. The reactor may be maintained at an elevated pressure such as at least approximately 2070 kPa or desirably at least approximately 2800 kPa. The temperature of the reaction mixture may be maintained at no more than 210° C. In the various embodiments described herein, the process may include: combining recycled effluent from the reactor with the feedstock, combining one or more oxidizing acids with the feedstock, comminuting the feedstock to reduce the size of the particles, feeding the feedstock into the high pressure reactor at an approximately constant feed rate, dispersing oxygen gas from the headspace of the reactor into the reaction mixture, and/or removing all or almost all of the gas from the reactor through the liquid effluent.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

U.S. Pat. No. 5,814,292, entitled “Comprehensive Energy ProducingMethods for Aqueous Phase Oxidation,” issued on 29 Sep. 1998, isincorporated herein by reference in its entirety. In the event of aconflict, the subject matter explicitly recited or shown herein controlsover any subject matter incorporated by reference. All definitions of aterm (express or implied) contained in any of the subject matterincorporated by reference herein are hereby disclaimed. The paragraphsshortly before the claims dictate the meaning to be given to any termexplicitly recited herein subject to the disclaimer in the precedingsentence.

BACKGROUND

A number of attempts have been made over the years to develop a processthat is capable of effectively and cost efficiently oxidizing a varietyof feed materials. Many of these processes were initially developed foruse in smelting or the removal of metal from ores. These processesconsumed large amounts of energy, emitted noxious gases, and rarelyachieved complete recovery of all the metals entering the process. Theywere also limited to very specific uses related to smelting, which madethem largely unsuitable for use with other feed materials.

Other processes have also been developed to oxidize various feedmaterials. One in particular was an aqueous phase oxidation process thatoxidized a feed material in a solution of nitric and sulfuric acid. Thereaction occurred in a pressurized reactor that was maintained at atemperature no greater than about 210° C. Oxygen gas was added toreoxidize a substantial portion of the reduction products of nitric acidthat were formed during oxidation of the feed materials.

Although this process was a significant advance over conventionaltechniques at the time, it still suffered from a number of problems. Forone, the process used a significant amount of oxygen gas to oxidize thereduction products of nitric acid. The oxygen gas was initially bubbledinto the aqueous phase but quickly separated and collected in theheadspace of the reactor where it was eventually removed. It wasnecessary to supply a large amount of oxygen gas to adequately oxygenatethe aqueous phase.

Another problem with this process concerned controlling the amount ofoxygen gas in the aqueous phase. It was difficult to directly measurethe amount of oxygen gas in the aqueous phase. However, it wasrelatively simple to measure the amount of oxygen gas in the headspace.Consequently, the amount of oxygen gas supplied to the reactor wascontrolled based on this measurement. Unfortunately, the amount ofoxygen gas in the headspace bore a tenuous relationship to the amount ofoxygen gas in the aqueous phase. It proved difficult to preciselycontrol the amount of oxygen gas supplied to the aqueous phase.

Other problems associated with this process were manifest when it wasattempted to operate it continuously. The reactor was highly pressurizedand the pressure fluctuated significantly over time. This made itdifficult to introduce feed material into the reactor at a constantrate. The feed material had a tendency to enter in spurts and pauses,which created problems controlling the reaction. Each time a spurt offeed material entered the reactor, a number of parameters would have tobe adjusted so that it could remain in the reactor long enough tocompletely oxidize.

The process was further complicated by variations in the physicalcharacteristics of the feed material, such as particle size, uniformity,moisture content, and the like. These problems were manifest by pluggingand clogging at various points up to and including entry into thereactor, unpredictable residence times and reaction rates, processcontrol difficulties, and the like. These problems resulted inoversizing the process equipment and extending the residence times totake into account the inconsistencies between the feed materials.

A number of embodiments of an improved aqueous phase oxidation processare described below. The improved process reduces or eliminates many ofthe problems and disadvantages associated with conventional aqueousphase oxidation processes.

SUMMARY

Various embodiments of an improved process for oxidizing a feedstock aredescribed herein. The process can be used to oxidize any suitableorganic or inorganic feedstock. In one embodiment, the process is usedto oxidize municipal and/or farm waste, e.g., dewatered sewage,municipal sludge cake, or animal manure.

The feedstock is oxidized in an aqueous reaction mixture by one or moreoxidizing acids. In one embodiment, the oxidizing acid is regenerated insitu. Oxygen gas may be supplied to the reaction mixture to reoxidizethe reduction products of the oxidizing acid. The reactor may bemaintained at suitable pressures and temperatures to facilitateregeneration of the oxidizing acid. Suitable oxidizing acids that may beused in the process include nitric acid and sulfuric acid.

In some embodiments, the feedstock may be processed before being fed tothe reactor to give it uniform physical properties and to render itbetter suited to be rapidly and efficiently oxidized. This processingmay include comminuting the feedstock so that the particles have auniform size that allows the feedstock to easily enter the reactor,combining the feedstock with recycled effluent from the reactor, and/orcombining the feedstock with one or more oxidizing acids before thefeedstock enters the reactor.

Once in the reactor, the feedstock is oxidized rapidly and efficiently.In some embodiments, gas from the headspace of the reactor, inparticular, oxygen gas, is dispersed into the reaction mixture. This maybe accomplished with a hollow impeller that causes gas from theheadspace to flow through the impeller and into the reaction mixture asthe impeller rotates. The result is that the composition of the gas inthe reaction mixture is close to or the same as the composition of thegas in the headspace. In particular, the concentration of oxygen gas inthe dissolved and undissolved gas portion of the reaction mixture issimilar, if not the same, as the concentration of the oxygen gas in theheadspace. The reaction mixture may be mixed vigorously to increase thetotal amount of oxygen gas the enters the mixture.

The gas in the reaction mixture may be removed as part of the liquideffluent stream. In other words, the gas that is dissolved andundissolved in the reaction mixture is removed with the reaction mixtureeffluent. A separate gas removal port on the reactor is unnecessary, butmay be provided for other purposes.

Once the effluent exits the reactor, it is cooled and the pressure isreduced to allow the gas to separate. The effluent may be vigorouslyagitated to speed up the separation and make it more complete. A portionof the effluent may be recycled back to the beginning of the process andcombined with the feedstock as mentioned above.

In one embodiment, the initial feedstock is combined with either or bothof the effluent from the reactor or one or more oxidizing acids to forma primary feedstock. The primary feedstock is fed into the reactor whereit is oxidized. The primary feedstock is part of the reaction mixturewhich also includes nitric acid and a secondary oxidizing acid.

In another embodiment, the initial feedstock is combined with either orboth of the effluent from the reactor or one or more oxidizing acids toform the primary feedstock. The primary feedstock is fed into thereactor where it is oxidized. The primary feedstock is part of thereaction mixture which also includes nitric acid and oxygen gas. Theoxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid. Thereaction mixture is maintained at a temperature that is no more thanapproximately 210° C.

In another embodiment, the initial feedstock is combined with either orboth of the effluent from the reactor or one or more oxidizing acids toform the primary feedstock. The primary feedstock is oxidized in thereactor. The primary feedstock is part of the reaction mixture whichalso includes nitric acid. The pressure in the reactor is maintained atat least approximately 2070 kPa.

In another embodiment, the initial feedstock is combined with either orboth of the effluent from the reactor or one or more oxidizing acids toform the primary feedstock. The primary feedstock is oxidized in thereactor. The primary feedstock is part of the reaction mixture whichalso includes nitric acid, a secondary oxidizing acid, and oxygen gas.The oxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid. Thereaction mixture is maintained at a temperature that is no more thanapproximately 210° C. The pressure in the reactor is maintained at atleast approximately 2070 kPa.

In another embodiment, the initial feedstock is comminuted to form theprimary feedstock where the largest dimension of at least approximately95% of the particles in the primary feedstock is no more than 7 mm. Theprimary feedstock is oxidized in the reactor where it is part of thereaction mixture which also includes nitric acid and the secondaryoxidizing acid.

In another embodiment, the initial feedstock is comminuted to form theprimary feedstock where the largest dimension of at least approximately95% of the particles in the primary feedstock is no more than 7 mm. Theprimary feedstock is oxidized in the reactor where it is part of thereaction mixture which also includes nitric acid and oxygen gas. Theoxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid. Thetemperature of the reaction mixture is maintained at no more thanapproximately 210° C.

In another embodiment, the initial feedstock is comminuted to form theprimary feedstock where the largest dimension of at least approximately95% of the particles in the primary feedstock is no more than 7 mm. Theprimary feedstock is oxidized in the reactor where it is part of thereaction mixture which also includes nitric acid. The pressure in thereactor is maintained at at least approximately 2070 kPa.

In another embodiment, the initial feedstock is comminuted to form theprimary feedstock where the largest dimension of at least approximately95% of the particles in the primary feedstock is no more than 7 mm. Theprimary feedstock is fed into the reactor at an approximately constantfeed rate and oxidized. The primary feedstock is part of the reactionmixture which also includes nitric acid, a secondary oxidizing acid, andoxygen gas. The oxygen gas is supplied to the reaction mixture in anamount that is sufficient to regenerate at least a majority of thenitric acid. The temperature of the reaction mixture is maintained at nomore than approximately 210° C. The pressure in the reactor ismaintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is fed into the reactor at a feedrate that is approximately constant. The feedstock is oxidized in thereactor where it is part the reaction mixture which also includes nitricacid and a secondary oxidizing acid. The pressure in the reactor ismaintained at at least approximately 2070 kPa. The feed rate isapproximately constant even though the pressure in the reactor may varyfrom approximately 2070 kPa to 6,900 kPa.

In another embodiment, the feedstock is fed into the reactor by afeeding device that is powered hydraulicly or by a gearmotor. Thefeedstock is oxidized in the reactor where it is part of the reactionmixture which also includes nitric acid and a secondary oxidizing acid.

In another embodiment, a first amount of the feedstock is fed into thepressurized reactor by the feeding device. The feeding device isisolated from the pressurized reactor and filled with a second amount ofthe feedstock. The second amount of the feedstock is fed into thepressurized reactor by the feeding device. The feedstock is oxidized inthe pressurized reactor where it is part of the reaction mixture whichalso includes nitric acid and a secondary oxidizing acid. The pressurein the reactor is maintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is fed into the reactor at a feedrate that is approximately constant. The feedstock is oxidized in thereactor where it is part of the reaction mixture which also includesnitric acid, a secondary oxidizing acid, and oxygen gas. The oxygen gasis supplied to the reaction mixture in an amount that is sufficient toregenerate at least a majority of the nitric acid. The temperature ofthe reaction mixture is maintained at no more than approximately 210° C.The pressure in the reactor is maintained at at least approximately 2070kPa. The feed rate is approximately constant even though the pressure inthe reactor may vary from approximately 2070 kPa to 6,900 kPa.

In another embodiment, the feedstock is fed into the reactor at a feedrate that fluctuates no more than approximately 10% per hour. Thefeedstock is oxidized in a reactor where it is part of the reactionmixture which also includes nitric acid. The pressure in the reactor ismaintained at at least approximately 2070 kPa. The feed rate fluctuatesno more than approximately 10% per hour even though the pressure in thereactor may vary from approximately 2070 kPa to 6,900 kPa.

In another embodiment, the feedstock is fed into the reactor with afeeding device that is powered hydraulicly or by a gearmotor. Thefeedstock is oxidized in the reactor where it is part of the reactionmixture which also includes nitric acid and oxygen gas. The oxygen gasis supplied to the reaction mixture in an amount that is sufficient toregenerate at least a majority of the nitric acid. The temperature ofthe reaction mixture is maintained at no more than approximately 210° C.

In another embodiment, the feedstock is fed into the reactor with afeeding device that is powered hydraulicly or by a gearmotor. Thefeedstock is oxidized in the reactor where it is part of the reactionmixture which also includes nitric acid. The pressure in the reactor ismaintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is fed into the reactor with afeeding device that is powered hydraulicly or by a gearmotor. Thefeedstock is oxidized in the reactor where it is part of the reactionmixture which also includes nitric acid, a secondary oxidizing acid, andoxygen gas. The oxygen gas is supplied to the reaction mixture in anamount that is sufficient to regenerate at least a majority of thenitric acid. The temperature of the reaction mixture is maintained at nomore than approximately 210° C. The pressure of the reactor ismaintained at at least approximately 2070 kPa.

In another embodiment, a first amount of the feedstock is fed into apressurized reactor by the feeding device. The feeding device isisolated from the pressurized reactor and filled with a second amount ofthe feedstock. The second amount of the feedstock is fed into thepressurized reactor by the feeding device. The feedstock is oxidized inthe pressurized reactor where it is part of the reaction mixture thatalso includes nitric acid. The pressure in the pressurized reactor ismaintained at at least approximately 2070 kPa. The first amount of thefeedstock and the second amount of the feedstock are fed into thepressurized reactor at a feed rate that fluctuates no more thanapproximately 10% per hour.

In another embodiment, a first amount of the feedstock is fed into thepressurized reactor by the feeding device. The feeding device isisolated from the pressurized reactor and filled with a second amount ofthe feedstock. The second amount of the feedstock is fed into thepressurized reactor by the feeding device. The feedstock is oxidized inthe pressurized reactor where it is part of the reaction mixture thatalso includes nitric acid, a secondary oxidizing acid, and oxygen gas.The temperature of the reaction mixture is maintained at no more thanapproximately 210° C. The pressure in the reactor is maintained at atleast approximately 2070 kPa. The first amount of the feedstock and thesecond amount of the feedstock are fed into the pressurized reactor at afeed rate that is approximately constant.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid and asecondary oxidizing acid. The gas from the headspace of the reactor isdispersed into the reaction mixture.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid andoxygen gas. The oxygen gas is supplied to the reactor and dispersed fromthe headspace into the reaction mixture in a manner that is sufficientto regenerate at least a majority of the nitric acid. The temperature ofthe reaction mixture is maintained at no more than approximately 210° C.

In another embodiment, the feedstock is oxidized in a reactor where itis part of the reaction mixture which also includes nitric acid and asecondary oxidizing acid. The concentration of dissolved and undissolvedoxygen gas in the gaseous portion of the reaction mixture is maintainedwithin approximately 25% of the concentration of oxygen gas in aheadspace of the reactor.

In another embodiment, the feedstock is oxidized in a reactor where itis part of the reaction mixture which also includes nitric acid, asecondary oxidizing acid, and oxygen gas. The oxygen gas is supplied tothe reactor and dispersed from the headspace of the reactor into thereaction mixture in a manner that is sufficient to regenerate at least amajority of the nitric acid. The temperature of the reaction mixture wasmaintained at no more than approximately 210° C. The pressure in thereactor was maintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is oxidized in a reactor where itis part of the reaction mixture which also includes nitric acid. Gasfrom the headspace of the reactor is dispersed into the reactionmixture. The pressure in the reactor is maintained at at leastapproximately 2070 kPa.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid andoxygen gas. The oxygen gas is supplied to the reactor mixture in anamount that is sufficient to regenerate at least a majority of thenitric acid. The concentration of dissolved and undissolved oxygen gasin the gaseous portion of the reaction mixture is maintained withinapproximately 25% of the concentration of oxygen gas in the headspace ofthe reactor. The temperature of the reaction mixture is maintained at nomore than approximately 210° C.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid. Theconcentration of dissolved and undissolved oxygen gas in the gaseousportion of the reaction mixture is maintained within approximately 25%of the concentration of oxygen gas in the headspace of the reactor. Thepressure in the reactor is maintained at at least approximately 2070kPa.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid, asecondary oxidizing acid, and oxygen gas. The oxygen gas is supplied tothe reaction mixture in an amount that is sufficient to regenerate atleast a majority of the nitric acid. The concentration of dissolved andundissolved oxygen gas in the gaseous portion of the reaction mixture ismaintained within approximately 25% of the concentration of oxygen gasin the headspace of the reactor. The temperature of the reaction mixtureis maintained at no more than approximately 210° C. The pressure in thereactor is maintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid and asecondary oxidizing acid. Gas is supplied to the reactor, and reactoreffluent is removed from the reactor. Also, at least approximately 94wt. % of the reaction mixture that exits the reactor does so in thereactor effluent, and at least approximately 94 wt. % of gas that exitsthe reactor does so in the reactor effluent.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid andoxygen gas. Gas, including oxygen gas, is supplied to the reactor. Thereactor effluent is removed from the reactor. The temperature of thereaction mixture is maintained at no more than approximately 210° C. Theoxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid Also, atleast approximately 94 wt. % of the reaction mixture that exits thereactor does so in the reactor effluent, and at least approximately 94wt. % of gas that exits the reactor does so in the reactor effluent.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid and asecondary oxidizing acid. Oxygen gas is supplied to the reactor, and thereactor effluent is removed from the reactor. The amount of oxygen gasin the reactor effluent is measured and the supply of oxygen gas to thereactor is adjusted based on the amount of oxygen gas measured in thereactor effluent.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid, asecondary oxidizing acid, and oxygen gas. Gas, including oxygen gas, issupplied to the reactor. Reactor effluent is removed from the reactor.The temperature of the reaction mixture is maintained at no more thanapproximately 210° C. The pressure in the reactor is maintained at atleast approximately 2070 kPa. The oxygen gas is supplied to the reactionmixture in an amount that is sufficient to regenerate at least amajority of the nitric acid. Also, at least approximately 94 wt. % ofthe reaction mixture that exits the reactor does so in the reactoreffluent, and at least approximately 94 wt. % of gas that exits thereactor does so in the reactor effluent.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid. Gas issupplied to the reactor, and the reactor effluent is removed from thereactor. The pressure in the reactor is maintained at at leastapproximately 2070 kPa. Also, at least approximately 94 wt. % of thereaction mixture that exits the reactor does so in the reactor effluent,at least approximately 94 wt. % of gas that exits the reactor does so inthe reactor effluent.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid andoxygen gas. The oxygen gas is supplied to the reactor in an amount thatis sufficient to regenerate at least a majority of the nitric acid. Thereactor effluent is removed from the reactor. The amount of oxygen gasin the reactor effluent is measured and the supply of oxygen gas isadjusted accordingly, The temperature of the reaction mixture ismaintained at no more than approximately 210° C.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid. Gas issupplied to the reactor, and the reactor effluent is removed from thereactor. The amount of oxygen gas in the reactor effluent is measuredand the supply of oxygen gas is adjusted accordingly. The pressure inthe reactor is maintained at at least approximately 2070 kPa.

In another embodiment, the feedstock is oxidized in the reactor where itis part of the reaction mixture which also includes nitric acid, asecondary oxidizing acid, and oxygen gas. The oxygen gas is supplied tothe reactor, and the reactor effluent is removed from the reactor. Theamount of oxygen gas in the reactor effluent is measured and the supplyof oxygen gas is adjusted accordingly. The temperature of the reactionmixture is maintained at no more than approximately 210° C. The pressurein the reactor is maintained at at least approximately 2070 kPa. Theoxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid.

It should be appreciated that all pressures referred to herein are gaugepressures unless stated otherwise. Also, all references to molarity aregiven at standard conditions for temperature and pressure—i.e., 0° C.and 101.325 kPa—unless stated otherwise.

The foregoing and other features, utilities, and advantages of thesubject matter described herein will be apparent from the following moreparticular description of certain embodiments as illustrated in theaccompanying drawings.

DRAWINGS

FIG. 1 is a block diagram of an improved aqueous phase oxidation processthat includes a feedstock processing system, a reaction system, and aneffluent processing system.

FIG. 2 is a block diagram of one embodiment of the feedstock processingsystem from FIG. 1.

FIG. 3 is a block diagram of another embodiment of the feedstockprocessing system from FIG. 1.

FIG. 4 is a block diagram of one embodiment of the reaction system fromFIG. 1.

FIG. 5 is a block diagram of one embodiment of the effluent processingsystem from FIG. 1.

DETAILED DESCRIPTION

The improved oxidation process, in its various embodiments, can be usedto oxidize a wide variety of materials. The process can be used tooxidize organic and/or inorganic material with very similar results inthe sense that the feed material is completely or nearly completelyoxidized, although the reaction products may be very different. Specificmaterials that may be oxidized using this process include, but are notlimited to, municipal and farm waste including dewatered sewage,municipal sludge cake and animal manure; slaughter house waste thatincludes blood, bone, and flesh; petroleum based wastes such asplastics, rubber, and paints; tires; wood pulp; hazardous materials suchas nerve gas, municipal garbage, and metal ore such as sulfidecontaining ores that are typically processed in smelters.

Although the process has a wide variety of uses, the followingdescription is provided primarily in the context of oxidizing sewageand/or manure based feedstocks. It should be appreciated, however, thatthe concepts and features described herein generally apply to theoxidation of other materials. Also, as each embodiment is described, itshould be understood that the features, advantages, characteristics,etc., of one embodiment may be applied to any other embodiment to formone or more additional embodiments unless noted otherwise. Furthermore,the principles, features, characteristics, and parameters described inthe U.S. Pat. No. 5,814,292, which is incorporated herein by reference,can be integrated into or substituted for various aspects of theimproved process.

Referring to FIG. 1, a block diagram of an improved aqueous phaseoxidation process 100 is shown. The process 100 includes a feedstockprocessing system 104, a reaction system 106, and an effluent processingsystem 108. The raw feedstock 102 enters the feedstock processing system104 where it is modified and/or processed in a number of ways to producea primary feedstock. The primary feedstock is fed to the reaction system106 where it is oxidized. The effluent from the reaction system 106enters the effluent processing system 108 where it is separated and/orotherwise processed to produce final products 110. Each system 104, 106,108 is described in greater detail.

The improved process is conceptually divided into the three systems 104,106, 108 for purposes of description. It should be appreciated, however,that the dividing line between each system 104, 106, 108 is somewhatarbitrary and does not represent a hard and fast boundary. Indeed,various components of one system could just as easily be considered partof a different system. With this in mind, the three systems 104, 106,108 should be viewed as nothing more than a conceptual framework fromwhich to describe the overall operation of the process.

As discussed above, the raw feedstock 102 may be any suitable feedstockthat is capable of being oxidized in the manner described herein. In oneembodiment, the feedstock is a sewage or manure based material that isapproximately 3% to 20% solids (e.g., 18% solids).

FIG. 2 shows a block diagram of one embodiment of the feedstockprocessing system 200. The raw feedstock 102 is initially mixed withrecycled effluent 204 to form an intermediate feedstock. The grinder 206comminutes the intermediate feedstock thereby forming a comminutedfeedstock. Comminuting the intermediate feedstock reduces the size ofthe particles and makes the intermediate feedstock more uniform.

The recycled effluent 204 may be combined with the raw feedstock 102 inthe grinder 206, as shown in FIG. 2, or before entering the grinder 206.If they are combined in the grinder 206, the grinding action may serveto mix the two materials together. If they are combined before enteringthe grinder 206, the recycled effluent 204 and the raw feedstock 102 maybe mixed in a separate vessel.

The recycled effluent 204 is added in an amount that is sufficient tocreate a slurry that doesn't plug or clog the grinder 206 and/orfacilitates later processing and transport. The amount of recycledeffluent 204 that is added may vary depending on the characteristics ofthe raw feedstock 102. Generally, larger quantities of the recycledeffluent 204 are used if the raw feedstock 102 is dry, while smallerquantities, or possibly none at all, are used if the raw feedstock 102already includes a suitable amount of liquid. It is also possible thatcertain feedstocks may be so wet that they must be dewatered beforeentering the process 100.

In certain embodiments, particularly those where the raw feedstock 102is sewage or manure based material, the volume ratio of the recycledeffluent 204 to the raw feedstock 102 in the intermediate feedstock maybe approximately 0.5 to 1.5 or, desirably, approximately 0.75 to 1.25.In one embodiment, approximately equal parts by volume of the recycledeffluent 204 and the raw feedstock 102 are combined to form theintermediate feedstock.

The recycled effluent 204 may be supplied at an elevated temperature sothat it heats the raw feedstock 102 when the two are mixed together. Theresulting intermediate feedstock may be significantly above ambienttemperature. The recycled effluent 204 may be supplied at a temperatureof approximately 40° C. to 90° C. or, desirably, 50° C. to 75° C. Forexample, the intermediate feedstock may be approximately 37° C. to 50°C.

As discussed in greater detail below, the effluent from reactor 402(FIG. 4) is heated by the exothermic oxidation of the feedstock. Therecycled effluent 204 may be at an elevated temperature simply becauseit has not cooled (either naturally or actively cooled) after leavingthe reactor 402. The recycled effluent 204 may also be heated in a heatexchanger to keep it at an elevated temperature. In one example,described in greater detail below, the recycled effluent 204 is heatedin a heat exchanger using heat from the effluent that has just left thereactor 402. The recycled effluent 204 may be stored in an insulatedtank or vessel before being mixed with the raw feedstock 102 to maintainit at an elevated temperature.

The intermediate feedstock is comminuted to reduce the particle sizes,improve the uniformity of the feedstock, make the feedstock moreamenable to evenly controlled pumping, and keep the solids suspended inthe slurry. This makes it easier to feed the feedstock into the reactor402, which is often operated at an elevated pressure, without pluggingthe entry opening.

The size and uniformity are also important because the reaction ratevaries significantly based on these factors, especially particle size.Larger particles generally need longer residence times to completelyoxidize. If the feedstock has both large and small particles, the largeparticles tend to dictate the residence time. Thus, it is desirable tocreate a feedstock that generally has small, uniform particles. This isespecially true when the feedstock includes organic matter such assewage and/or manure.

Increasing the reaction rate by comminuting the feedstock makes itpossible to reduce the size of the reactor 402 and/or increase the feedrate of the feedstock into the reactor 402. Either adjustment has abeneficial effect on the economics of the process 100.

In one embodiment, the largest dimension of at least approximately 95%of the particles in the comminuted feedstock is no more than 7 mm, nomore than 4 mm, no more than 2.5 mm, desirably, no more than 1.5 mm, or,suitably, no more than 0.5 mm. In another embodiment, the largestdimension of at least approximately 98% of the particles in thecomminuted feedstock is no more than 7 mm, no more than 4 mm, no morethan 2.5 mm, desirably, no more than 1.5 mm, or, suitably, no more than0.5 mm. In yet another embodiment, the largest dimension of at leastsubstantially all of the particles in the comminuted feedstock is nomore than 7 mm, no more than 4 mm, no more than 2.5 mm, desirably, nomore than 1.5 mm, or, suitably, no more than 0.5 mm.

Returning to FIG. 2, the comminuted feedstock moves from the grinder 206to a mixing vessel 208 where it is combined with a primary oxidizingacid or first acid 210 and a secondary oxidizing acid or second acid 212to form a primary feedstock. Additional amounts of the recycled effluent204 may be combined in the vessel 208 to produce the desiredconcentration of the acids 210, 212 or to alter the consistency or otherproperties of the feedstock.

It has been found that pre-treating the feedstock in this mannerincreases the rate of the redox reaction in the reactor 402,particularly for feedstock that includes organic matter such as sewageand/or manure. The acids 210, 212 initiate de-lignination of the organicfibers and other organic matter in the primary feedstock. De-ligninationis beneficial because it further reduces the size of the particles inthe feedstock and exposes them to chemical attack in the reaction system106.

In the embodiment shown in FIG. 2, de-lignination begins when therecycled effluent 204, which includes the acids 210, 212, is firstcombined with the raw feedstock 102. Thus, de-lignination is initiatedwhen the recycled effluent 204 is combined with the raw feedstock 102 inthe grinder 206 and accelerates when the additional acids 210, 212 areadded in the vessel 208.

The primary oxidizing acid 210 and the secondary oxidizing acid 212 areadded until the concentration of the acids 210, 212 in the primaryfeedstock, excluding solids (i.e., the concentration of the primaryfeedstock excluding the solids portion), is approximately the same asthe concentration of the acids 210, 212, respectively, in the reactor402 at start-up.

The primary oxidizing acid 210 may be nitric acid, and the secondaryoxidizing acid 212 may be sulfuric acid. The nitric acid functions asthe oxidizing agent to oxidize the feedstock. The nitric acid isincluded in an amount that is sufficient to rapidly and completelyoxidize the feedstock.

The sulfate ions of the sulfuric acid convert the salt forming reactionproducts into stable sulfate salts, thereby leaving the nitric acid inthe acid state to continue as the primary oxidant. The sulfate reactswith nitrogen containing compounds to prevent the formation of ammoniumnitrate, an explosive, and/or other undesirable reaction products.Instead, the sulfate reacts with nitrogen compounds to form ammoniumsulfate. The sulfuric acid is provided in an amount that is sufficientto prevent the formation of ammonium nitrate, but not enough toprecipitate sulfur or volatilize significant amounts of the sulfuricacid.

In one embodiment, the nitric acid may be added to achieve aconcentration in the primary feedstock, excluding solids, of at leastapproximately 0.08 mol/L, desirably, at least approximately 0.5 mol/L,or, suitably, at least approximately 0.84 mol/L. In another embodiment,the nitric acid may be added to achieve a concentration in the primaryfeedstock, excluding solids, of no more than approximately 4.2 mol/L,desirably, no more than approximately 3.3 mol/L, or, suitably, no morethan approximately 2.5 mol/L. In yet another embodiment, the nitric acidmay be added to achieve a concentration in the primary feedstock,excluding solids, of approximately 0.08 mol/L to 4.2 mol/L, desirably,approximately 0.5 mol/L to 3.3 mol/L, or, suitably, approximately 0.84mol/L to 2.5 mol/L.

On a weight basis, the nitric acid may be added to achieve aconcentration in the primary feedstock, excluding solids, of at leastapproximately 0.5 wt. %, desirably, at least approximately 3 wt. %, or,suitably, at least approximately 5 wt. %. In another embodiment, thenitric acid may be added to achieve a concentration in the primaryfeedstock, excluding solids, of no more than approximately 25 wt. %,desirably, no more than approximately 20 wt. %, or, suitably, no morethan approximately 15 wt. %. In yet another embodiment, the nitric acidmay be added to achieve a concentration in the primary feedstock,excluding solids, of approximately 0.5 wt. % to 25 wt. %, desirably,approximately 3 wt. % to 20 wt. %, or, suitably, approximately 5 wt. %to 15 wt. %.

With regard to sulfuric acid, in one embodiment, the sulfuric acid maybe added to achieve a concentration in the primary feedstock, excludingsolids, of at least approximately 0.1 mol/L, desirably, at leastapproximately 0.12 mol/L, or, suitably, at least approximately 0.16mol/L. In another embodiment, the sulfuric acid may be added to achievea concentration in the primary feedstock, excluding solids, of no morethan approximately 1 mol/L, desirably, no more than approximately 0.54mol/L, or, suitably, no more than approximately 0.32 mol/L. In yetanother embodiment, the sulfuric acid may be added to achieve aconcentration in the primary feedstock, excluding solids, ofapproximately 0.1 mol/L to 1 mol/L, desirably, approximately 0.12 mol/Lto 0.54 mol/L, or, suitably, approximately 0.16 mol/L to 0.32 mol/L.

On a weight basis, the sulfuric acid may be added to achieve aconcentration in the primary feedstock, excluding solids, of at leastapproximately 0.9 wt. %, desirably, at least approximately 1.1 wt. %,or, suitably, at least approximately 1.5 wt. %. In another embodiment,the sulfuric acid may be added to achieve a concentration in the primaryfeedstock, excluding solids, of no more than approximately 10 wt. %,desirably, no more than approximately 5 wt. %, or, suitably, no morethan approximately 3 wt. %. In yet another embodiment, the sulfuric acidmay be added to achieve a concentration in the primary feedstock,excluding solids, of approximately 0.9 wt. % to 10 wt. %, desirably,approximately 1.1 wt. % to 5 wt. %, or, suitably, approximately 1.5 wt.% to 3 wt. %.

The mixing vessel 208 may be any suitable tank, pipe, or other vesselthat is capable of holding and/or mixing the materials. The mixingvessel 208 should be made of a material that is chemically resistant tothe acids 210, 212. Suitable materials include plastic, stainless steel,titanium, or the like. In an alternate embodiment, the grinder 206 andthe mixing vessel 208 may be combined together so that everything iscomminuted and/or mixed in the same vessel.

As shown in FIG. 2, the primary feedstock exits the mixing vessel 208and is stored in a storage vessel or tank 214 before it is fed into thereactor 402. In one embodiment, the storage vessel 214 may be insulatedto maintain the temperature of the primary feedstock and conserveenergy. It should be noted that it is generally not desirable to storethe primary feedstock for a long period of time before feeding it intothe reactor 402. The presence of the acids 210, 212 may cause theprimary feedstock to separate and the texture to change in a way thatcan make it difficult to feed into the reactor 402.

The primary feedstock is now prepared to be fed into the reactor 402.This is accomplished using one or more feeding devices 216. In oneembodiment, the primary feedstock is transferred to the feeding device216 via a low pressure pump and a combination of vacuum and gravityflow. It should be appreciated, however, that any suitable method may beused to transfer the primary feedstock to the feeding device 216.

The feeding device 216 is used to feed the primary feedstock into thereactor 402 at a steady rate. It has been discovered that relativelyminor fluctuations in the feed rate can cause large fluctuations in theredox reaction. If the feed rate drops, the reactor 402 is starved andif the feed rate climbs, the reactor 402 is overfed.

The redox reaction is much more sensitive to feed rate fluctuations thanit is to other parameters such as temperature and pressure. For thisreason, it is desirable to tightly control the feed rate. However, thisis not a simple matter since the reactor 402 experiences relativelylarge fluctuations in pressure and temperature. The pressure swings makeit particularly difficult to feed the primary feedstock into the reactor402 at a steady rate.

The feeding device 216 may have any suitable configuration that allowsit to feed the primary feedstock at a steady rate. In one embodiment,the feeding device 216 is actuated or powered hydraulicly. For example,the feeding device 216 may include one or more hydraulic rams thatdispense or force the primary feedstock into the reactor 402. Oneexample of a suitable hydraulicly powered feeding device is a cyclingram pump.

In another embodiment, the feeding device 216 is actuated or powered bya gearmotor. For example, the feeding device 216 includes a gearmotorthat turns a screw which, in turn, feeds the primary feedstock into thereactor 402. The feeding device 216 may be configured so that pressurefluctuations in the reactor 402, even up to the reactor's safe operatingpressure limit of approximately 13,800 kPa, do not significantly changethe feed rate.

In one embodiment, the feeding device 216 is an extruder and/or injectorthat is hydraulically or gear actuated. Multiple feeding devices 216 maybe used to provide an uninterrupted supply of the primary feedstock tothe reactor 402. The multiple feeding devices 216 may be sequentiallyactivated and refilled. When one feeding device 216 is injecting thefeedstock into the reactor 402, another feeding device 216 may berefilled with the primary feedstock. Also, the use of multiple feedingdevices 216 is advantageous because it allows one or more devices 216 tobe offline for maintenance or repairs while the remainder of the devices216 provide a continuous supply of feedstock to the reactor 402.

The feeding device 216 may feed the primary feedstock into the reactorat a rate that fluctuates no more than approximately 10% per hour,desirably, no more than approximately 5% per hour, or, suitably no morethan approximately 2% per hour. In another embodiment, the feedingdevice 216 feeds the primary feedstock into the reactor at a feed ratethat is approximately constant. The feeding device 216 is capable ofmaintaining these feed rates even though the pressure in the reactor 402may vary from approximately 2070 kPa to 6,900 kPa.

The feeding device 216 is exposed to the high pressure of the reactor402 when it is feeding the primary feedstock into the reactor 402.However, the feeding device 216 is at a low pressure when it is filledwith the primary feedstock from the storage vessel 214. The valves 218,220 may be used to selectively isolate the feeding device 216 from thereactor 402 during feeding and refilling operations. The valve 218 isclosed and the valve 220 is open when the feeding device 216 injects theprimary feedstock into the reactor 402. The valve 220 is closed and thevalve 218 is open when the feeding device 216 is refilled with theprimary feedstock.

The valves 218, 220 may also be used to isolate the feeding device 216so that it can be repaired while the reactor 402 remains in operation.Moreover, the valves 218, 220 can also prevent backflow from the reactor402 into the feedstock processing system 104 during an overpressureevent. It should be appreciated that although the valves 218, 220 aredepicted as being separate from the feeding device 216, the valves 218,220 may be provided as integral components of the feeding device 216.

A pressure release system 222 may be provided that allows the feedingdevice 216 to transition from a high pressure state to a low pressurestate without causing undue wear on the components and/or blowback intothe mixing vessel 208 when the valve 218 is opened. In one embodiment,the pressure release system may include a tank that is capable ofabsorbing excess pressure.

It should be appreciated that the feedstock processing system 104 may beconfigured in a number of other ways besides what is shown in FIG. 2.For example, FIG. 3 shows a block diagram of another embodiment of afeedstock processing system 300. This embodiment is similar to thefeedstock processing system 200 except that the raw feedstock does notenter a grinder before entering the mixing vessel 208. Also, the primaryfeedstock is not stored in a separate storage vessel.

The feedstock processing system 300 may be suitable for situations wherethe raw feedstock 102 does not need to be comminuted. For example, theraw feedstock 102 may already be uniform with small particles. Also, themixing vessel 208 may function as a storage vessel so that the primaryfeedstock is drawn from the mixing vessel 208 into the reactor 402.Numerous other changes to the feedstock processing system 104 are alsocontemplated.

Referring to FIG. 4, a block diagram is shown of one embodiment of areaction system 400. The reaction system 400 includes the reactor 402,which receives the processed feedstock from the feedstock processingsystem 104. The reactor 402 is in fluid communication with a make-upacid source 404, an oxygen gas source 406, a control gas source 408, anda recycled gas source 410. The reactor 402 includes one or more sensors412 and an impeller or dispersion device 414. The temperature of thereactor 402 may be controlled by an energy control system 416.

At start-up, the reactor 402 is initially charged with an initialreaction mixture that includes an aqueous solution of the primaryoxidizing acid and the secondary oxidizing acid. In one embodiment, theprimary oxidizing acid is nitric acid and the secondary oxidizing acidis sulfuric acid. The reactor 402 may be initially charged with anaqueous mixture of nitric and sulfuric acid having any of theconcentrations described above. For example, equal volumes ofapproximately 3.35 mol/L nitric acid and 0.4 mol/L sulfuric acid may becombined in the reactor 402 to form the initial reaction mixture.

The reactor 402 may be filled to any suitable level with the initialreaction mixture. In one embodiment, the initial reaction mixtureoccupies at least approximately 25% of the volume of the reactor 402 or,suitably, at least approximately 35% of the volume of the reactor. Inanother embodiment, the initial reaction mixture occupies no more thanapproximately 80% of the volume of the reactor 402 or, suitably, no morethan approximately 70% of the volume of the reactor 402. In yet anotherembodiment, the initial reaction mixture occupies approximately 25% to80% of the volume of the reactor 402 or, suitably, approximately 35% to70% of the volume of the reactor 402. Preferably, the initial reactionmixture occupies approximately 50% of the volume of the reactor 402. Inany of these embodiments, the remainder of the volume of the reactor402, i.e., the headspace, is occupied by gases.

The headspace is initially charged with oxygen gas and/or one or moreother gases, preferably inert gases. The oxygen gas is used toregenerate the nitric acid in the reaction mixture as described ingreater detail below. The oxygen gas 406 may be supplied from anysuitable source. For example, the oxygen source may be air, pure oxygen,or even a product of another reaction.

In one embodiment, the gas in the headspace at start-up includes atleast approximately 2 volume percent oxygen gas, desirably, at leastapproximately 5 volume percent, or, suitably, at least approximately 8volume percent. In another embodiment, the gas in the headspace atstart-up includes no more than approximately 60 volume percent oxygengas, desirably, no more than approximately 45 volume percent oxygen gas,or, suitably, no more than approximately 35 volume percent oxygen gas.In yet another embodiment, the gas in the headspace at start-up includesapproximately 2 to 60 volume percent oxygen gas, desirably, 5 to 45volume percent oxygen gas, or, suitably, 8 to 35 volume percent oxygengas.

The headspace may also be charged with other gases that are inert orotherwise unable to adversely affect the redox reaction. Suitable gasesinclude nitrogen, argon, and the like. These gases are supplied as thecontrol gas 408 in FIG. 4.

At start-up, the temperature and pressure are increased together untiloperating conditions are reached. For example, when the temperaturereaches 60° C., the pressure is increased (by adding gas to theheadspace) to approximately 1035 kPa. At 150° C., the pressure isincreased to approximately 2070 kPa. Once the mixture reaches operatingtemperature, the pressure is increased to approximately 3450 kPa. Itshould be appreciated, that the temperature and pressure may fluctuatesubstantially from the initial levels during processing.

The initial reaction mixture is heated by the energy control system toat least 150° C. as the impeller 414 vigorously mixes or agitates thereaction mixture. The reactor 402 may be heated using a heat exchangerin the energy control system 416 that is in fluid communication with aheating jacket on the outside of the reactor 402. It should beappreciated that in most situations the reactor 402 only needs to beheated at start-up. Once the redox reaction begins, it is sufficientlyexothermic that it is unnecessary to continue heating the reactor 402during operation. Instead, the reactor 402 may include an internalcooling coil that is used to maintain the temperature of the reactionmixture below a maximum threshold. It should be appreciated that thesame coil may be used to heat and cool the reactor 402, if desired.

It should be appreciated that the energy control system 416 can beviewed as a collection of any number, type, or configuration of heatexchangers, heat sources, heat sinks and other energy transfer devicesand components that can be used to add and/or extract heat from variousstreams, reactors, etc. For example, the energy control system 416 mayinclude a supplemental heat source that is used to supply and/or removeheat from the heat exchanger using one or more heat exchange coils.Numerous other examples are also contemplated.

The impeller 414 is used to thoroughly and vigorously mix the reactionmixture and disperse the gas from the headspace into the reactionmixture. The impeller 414 may have any suitable design or configurationso long as it is capable of adequately doing these things. In oneembodiment, the impeller may be a gas entrainment impeller. The gas isdispersed by impeller blades attached to a hollow shaft through whichgases are continuously recirculated from the headspace of the reactor402. The gas enters openings near the top of the shaft and is expelledthrough dispersion ports located at the tips of the impeller blades. Thehigh speed rotation of the impeller blades creates a low pressure areaat the tip. The pressure at the tip of the blades drops as the speed ofthe impeller 414 increases, thereby increasing the rate at which gas isdispersed from the headspace through the reaction mixture.

The reactor 402 may also include one or more baffles that enhancedispersion of the headspace gas as well as the general stirring of thereaction mixture. The transfer of gas is governed by the relative speedof the tips of the impeller 414 to the liquid phase, which reduces thepressure at the tips (i.e., creates a vacuum) of the impeller 414 andthereby draws gas into the reaction mixture. A baffle may be used toimpede rotation of the liquid reaction mixture relative to the impeller414. This may enhance the operation of the impeller 414. A baffledesigned specifically for this purpose may be placed in the reactor 402.Alternatively, the cooling coil and/or other structures that areintegral or added to the reactor 402 may function as a baffle. In oneembodiment, the cooling coil may have a serpentine shape.

The sensors 412 may measure one or more of the following parameters:temperature, pressure, or liquid level. The sensors 412 may be used toimplement an automated control system or simply provide the operatorwith information about the status of the reactor 402. The reactor 402may have an emergency blowdown system as well as a gas out port.

The emergency blowdown system includes a large-diameter, high pressurepipe that runs from the reactor 402 to an emergency blowdown containmentvessel. In the event of an emergency overheat/overpressure situation,the pipe will quickly empty the reactor 402 into the emergency blowdowncontainment vessel. The vessel will receive all the contents of thereactor 402 without leaking anything to the surrounding environment.

The gas out port is not ordinarily used to remove the gas from thereactor 402. Instead, the gas is primarily removed in the reactoreffluent. The reactor 402 may be any suitable size that is capable ofaccommodating the desired throughput.

Once the reactor 402 reaches its start-up parameters, it is ready tobegin receiving and oxidizing the primary feedstock. Shortly after theprimary feedstock enters the reactor 402, the redox reaction reaches asteady operating state. At this point, the reaction mixture includes theprimary feedstock, the initial start-up oxidizing acids, water,dissolved and undissolved gases as well as various reaction products.The redox reaction can be indefinitely sustained at a steady state.Although conditions in the reactor 402 may vary significantly over time,they do not vary so much that the reaction is adversely affected.

In some respects, the start-up parameters of the reactor 402, such asthe oxygen gas concentration in the headspace and the volume occupied bythe reaction mixture, are maintained during operation. For example, theoxygen gas concentrations are maintained at the levels described aboveduring operation. Also, the reaction mixture may occupy the same volumeof the reactor 402 as the initial reaction mixture. Thus, the volumeamounts described above in connection with the initial reaction mixtureapply equally to the reaction mixture during operation.

The pressure in the reactor 402 is maintained at a level that issufficient to keep the reaction products of nitric acid in solution sothat they can react with the oxygen to regenerate the nitric acid. Inone embodiment, the pressure in the reactor 402 is maintained at atleast approximately 2070 kPa, desirably, at least approximately 2410kPa, or, suitably, at least approximately 2800 kPa. In anotherembodiment, the pressure in the reactor 402 is maintained at no morethan approximately 6900 kPa, desirably, no more than approximately 6200kPa, or, suitably, no more than approximately 5515 kPa. In yet anotherembodiment, the pressure in the reactor 402 is maintained atapproximately 2070 kPa to 6900 kPa, desirably, approximately 2410 kPa to6200 kPa, or, suitably, approximately 2800 kPa to 5515 kPa.

The pressure in the reactor 402 may be maintained by selectively addingthe oxygen gas 406, the control gas 408, or the recycled gas 410. If theconcentration of oxygen gas 406 is low, then oxygen gas 406 is added toincrease the pressure. However, if additional oxygen gas 406 is notneeded, then either the control gas 408 or the recycled gas 410 areadded to increase the pressure. It should be understood that the redoxreaction generates gas that also contributes to the pressure inside thereactor 402. Due to the high operating pressure of the reactor 402, theoxygen gas 406, the control gas 408, and/or the recycled gas 410 may besupplied at pressures greater than 6900 kPa so that they will flow intothe reactor 402.

The temperature of the reaction mixture is maintained at a level thatprevents the nitric acid from decomposing, but encourages the rapidoxidation of the feedstock. The temperature is controlled with theenergy control system 416 as described above. In one embodiment, thetemperature of the reaction mixture is maintained at no more than 210°C. or, desirably, no more than 205° C. In another embodiment, thetemperature of the reaction mixture is maintained at at leastapproximately 150° C. or, desirably, approximately 160° C. In yetanother embodiment, the temperature of the reaction mixture ismaintained at approximately 150° C. to 210° C., or, desirably,approximately 160° C. to 205° C.

During operation, the impeller 414 is configured to disperse asufficient amount of the oxygen gas from the headspace into the reactionmixture to regenerate the nitric acid. The oxygen reacts with the nitricacid reduction products to form nitric acid without any processingoutside of the reactor. The amount of the nitric acid that isregenerated can vary. In one embodiment, at least a majority of thenitric acid is regenerated, desirably, at least 75% of the nitric acidis regenerated, or, suitably at least 90% of the nitric acid isregenerated.

The impeller 414 circulates the gas from the headspace through thereaction mixture so that the concentration of the gases in the reactionmixture is very similar, if not the same, as the concentration of thegases that are dissolved or undissolved in the reaction mixture. Theadvantage of this is that the amount of oxygen gas supplied to thereaction mixture can be closely controlled based on oxygen gasmeasurements taken in the headspace. In one embodiment, concentration ofdissolved and undissolved oxygen gas in the gaseous portion of thereaction mixture is within approximately 25% of the concentration ofoxygen gas in the headspace, desirably, within approximately 10% of theconcentration of oxygen gas in the headspace, or, suitably, withinapproximately 5% of the concentration of oxygen gas in the headspace.

The composition of the gas in the headspace may be adjusted to controlthe reaction products produced by the redox reaction. Preferably, thedesired reaction products are maximized when the composition of gasesinside the reactor meet the following parameters: oxygen has theconcentration given above, carbon dioxide 5%-25% by volume; carbonmonoxide 2%-10% by volume; nitrous oxide (N₂O) 2%-5% by volume with theremainder being Argon and/or Nitrogen as well as minor amounts of NO_(x)and SO_(x) as trace impurities.

The concentration of the oxidizing acids in the reaction mixture may bethe same or similar to the concentration at start-up. Additional acid isadded from the make-up acid source 404 as needed.

Inside the reactor 402, the feedstock undergoes a complex, exothermic,redox process. The nitrogen compounds in the reaction mixture arealtered so that the nitrogen compounds are reduced to gaseous nitrogenand/or nitrous oxide (N₂O). Except those already listed, no compounds ofthe NO_(x) type are produced in the reaction mixture at more than tracelevels. A portion of the nitrogen compounds in the reaction mixture isincorporated into the complex hydrocarbons noted below.

A substantial portion of the carbon in the feedstock is oxidized tocarbon dioxide and/or carbon monoxide. That portion of the carbon in thefeedstock that is not oxidized to either carbon dioxide or carbonmonoxide is incorporated into heavier hydrocarbon molecules. Insituations where the oxidation potential was held to a sustained lowlevel, a portion of the carbon in the feedstock was reduced tofuranones, and furandiones, as well as other complex hydrocarbons suchas paraffins.

The hydrogen in the reaction mixture is oxidized primarily to water.However, in certain conditions, the hydrogen may be incorporated intocomplex hydrocarbons such as organic hydrofluorides of the typeamine-dihydrofluoride. Other minor/trace components such as phosphorous,potassium, ammonia, iron, and the like, form sulfates, nitrates, as wellas other, more complex, salts.

A reactor effluent may be continually extracted from the reactor 402.The reactor effluent primarily includes salty, acidic water (and in someembodiments, minor levels of complex hydrocarbons as noted above) sincethat is all that is left when the reaction is complete. In oneembodiment, most, if not all, of the gas that is removed from thereactor 402 exits with the reactor effluent. The gas that exits with theeffluent is the dissolved and undissolved gas in the reactionmixture—i.e., the gaseous portion of the reaction mixture.

In one embodiment, at least approximately 94 wt. % of the reactionmixture that exits the reactor 402 does so in the reactor effluent, andat least approximately 94 wt. % of the gas that exits the reactor doesso in the reactor effluent. In another embodiment, at leastapproximately 98 wt. % of the reaction mixture that exits the reactor402 does so in the reactor effluent, and at least approximately 98 wt. %of the gas that exits the reactor does so in the reactor effluent. Inyet another embodiment, at least substantially all of the reactionmixture that exits the reactor 402 does so in the reactor effluent, andat least approximately substantially all of the gas that exits thereactor does so in the reactor effluent.

Upon exiting the reactor 402, the effluent may enter the energy controlsystem 416. The energy control system 416 serves two primary functions:to extract energy from the process and to maintain the operatingtemperature of the reactor 402. Energy can be extracted by allowing theeffluent to flow to a slightly reduced pressure heat exchanger whichtransfers energy to harness it for productive ends. The second functionis accomplished as described above.

It should be noted that any unspent nitric acid in the reactor effluentmay be removed by flashing it off before it is cooled below the boilingpoint of nitric acid. Also, any excess water may be flashed off in theenergy control system. The need to flash or otherwise separate waterfrom the effluent may be reduced by restricting the amount of water thatis added to the feedstock.

Turning to FIG. 5, a block diagram of one embodiment of an effluentprocessing system 500 is shown. The effluent processing system 500receives the effluent after it exits the energy control system 416. Anumber of sensors 506 are used to measure parameters such as pH andconductivity of the cooled effluent. This information may be used tocontrol the amount of the acids 210, 212 that are added to the mixingvessel 208. For example, the lower the pH of the effluent, the less acidthat needs to be added to the mixing vessel 208.

The cooled effluent flows to the gas separation system 502 where thepressure is allowed to drop to ambient inside the separation equipment.At this point, the effluent is vigorously agitated to drive off thedissolved and undissolved gases. From the gas separation system 502, theliquid/solids stream is split with a portion of the stream going to amixing area 510 and a portion going to the solids separation system 504.From solids separation system 504, the stream is split with part goingto the mixing area 510 and the remainder going to the waste watertreatment 514. From the mixing area 510, the effluent is recycled backto the feedstock processing system 104. As shown in FIG. 4, the recycledeffluent may be heated in the energy control system 416 before itreaches the feedstock processing system 104. The solids recovered fromthe solids separation system 504 are sent to post processing forrefining into final solid products, which can are then stored, packaged,shipped and/or disposed.

The gases move from the gas separation system 502 through sensors 508and on to either be recycled back to the reactor 402 or to the gasprocessing system 516. The different gases are separated in the gasprocessing system 516. From the gas processing system 516, the oxygen,plus the amounts of argon/nitrogen needed for the reactor 402 are pumpedinto a pressured holding tank. At the gas processing system, the gasesnot required for the reactor 402 are processed and moved to the finalgas products 518 for storing, packaging, shipping and/or disposal.

Illustrative Embodiments

Reference is made in the following to a number of illustrativeembodiments of the subject matter described herein. The followingembodiments illustrate only a few selected embodiments that may includethe various features, characteristics, and advantages of the subjectmatter as presently described. Accordingly, the following embodimentsshould not be considered as being comprehensive of all of the possibleembodiments. Also, features and characteristics of one embodiment mayand should be interpreted to equally apply to other embodiments or beused in combination with any number of other features from the variousembodiments to provide further additional embodiments, which maydescribe subject matter having a scope that varies (e.g., broader, etc.)from the particular embodiments explained below. Accordingly, anycombination of any of the subject matter described herein iscontemplated.

According to one embodiment, a method comprises: combining an initialfeedstock and effluent from a reactor to form a primary feedstock; andoxidizing the primary feedstock in the reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid and asecondary oxidizing acid. The method may comprise comminuting theprimary feedstock. The method may comprise combining the initialfeedstock, the effluent, and an oxidizing acid to form the primaryfeedstock. The method may comprise combining the initial feedstock, theeffluent, nitric acid, and the secondary oxidizing acid to form theprimary feedstock, and wherein the concentration of nitric acid and thesecondary oxidizing acid in the primary feedstock, excluding solids, maybe approximately the same as the concentration of the nitric acid andthe secondary oxidizing acid, respectively, in the reactor at start-up.The primary feedstock may include particles where the largest dimensionof at least approximately 95% of the particles in the primary feedstockis no more than 4 mm. The effluent may be at a temperature that iselevated relative to the ambient temperature. The effluent may beacidic.

According to another embodiment, a method comprises: combining aninitial feedstock and effluent from a reactor to form a primaryfeedstock; oxidizing the primary feedstock in the reactor, the primaryfeedstock being part of a reaction mixture that also includes nitricacid and oxygen gas; supplying the oxygen gas to the reaction mixture inan amount that is sufficient to regenerate at least a majority of thenitric acid; and maintaining the reaction mixture at a temperature thatis no more than approximately 210° C. The method may comprisecomminuting the primary feedstock. The method may comprise combining theinitial feedstock, the effluent, and an oxidizing acid to form theprimary feedstock. The method may comprise combining the initialfeedstock, the effluent, nitric acid, and a secondary oxidizing acid toform the primary feedstock, and wherein the concentration of nitric acidand the secondary oxidizing acid in the primary feedstock, excludingsolids, may be approximately the same as the concentration of the nitricacid and the secondary oxidizing acid, respectively, in the reactor atstart-up. The primary feedstock may includes particles where the largestdimension of at least approximately 95% of the particles in the primaryfeedstock is no more than 4 mm. The effluent may be at a temperaturethat is elevated relative to the ambient temperature.

According to another embodiment, a method comprises: combining aninitial feedstock and an oxidizing acid to form a primary feedstock;oxidizing the primary feedstock in a reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid andoxygen gas; supplying the oxygen gas to the reaction mixture in anamount that is sufficient to regenerate at least a majority of thenitric acid; and maintaining the reaction mixture at a temperature thatis no more than approximately 210° C. The method may comprisecomminuting the primary feedstock. The oxidizing acid may be a primaryoxidizing acid, and the method may comprise combining the initialfeedstock, the primary oxidizing acid, and a secondary oxidizing acid toform the primary feedstock. The concentration of the primary oxidizingacid and the secondary oxidizing acid in the primary feedstock,excluding solids, may be approximately the same as the concentration ofthe nitric acid and the secondary oxidizing acid, respectively, in thereactor at start-up. The primary feedstock may include particles wherethe largest dimension of at least approximately 95% of the particles inthe primary feedstock is no more than 4 mm. The oxidizing acid mayinclude nitric acid.

According to another embodiment, a method comprises: combining aninitial feedstock and effluent from a reactor to form a primaryfeedstock; oxidizing the primary feedstock in the reactor, the primaryfeedstock being part of a reaction mixture that also includes nitricacid; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa. The method may comprise comminuting the primaryfeedstock. The method may comprise combining the initial feedstock, theeffluent, and an oxidizing acid to form the primary feedstock. Themethod may comprise combining the initial feedstock, the effluent,nitric acid, and a secondary oxidizing acid to form the primaryfeedstock, and wherein the concentration of nitric acid and thesecondary oxidizing acid in the primary feedstock, excluding solids, maybe approximately the same as the concentration of the nitric acid andthe secondary oxidizing acid, respectively, in the reactor at start-up.The primary feedstock may include particles where the largest dimensionof at least approximately 95% of the particles in the primary feedstockis no more than 4 mm. The pressure in the reactor may be at least 2800kPa.

According to another embodiment, a method comprises: combining aninitial feedstock and an oxidizing acid to form a primary feedstock; andoxidizing the primary feedstock in a reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid and asecondary oxidizing acid.

According to another embodiment, a method comprises: combining aninitial feedstock and an oxidizing acid to form a primary feedstock;oxidizing the primary feedstock in a reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid; andmaintaining a pressure in the reactor of at least approximately 2070kPa.

According to another embodiment, a method comprises: combining aninitial feedstock and effluent from a reactor to form a primaryfeedstock; oxidizing the primary feedstock in the reactor, the primaryfeedstock being part of a reaction mixture that also includes nitricacid, a secondary oxidizing acid, and oxygen gas; supplying the oxygengas to the reaction mixture in an amount that is sufficient toregenerate at least a majority of the nitric acid; maintaining thereaction mixture at a temperature that is no more than approximately210° C.; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa.

According to another embodiment, a method comprises: combining aninitial feedstock and an oxidizing acid to form a primary feedstock;oxidizing the primary feedstock in a reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid, asecondary oxidizing acid, and oxygen gas; supplying the oxygen gas tothe reaction mixture in an amount that is sufficient to regenerate atleast a majority of the nitric acid; maintaining the reaction mixture ata temperature that is no more than approximately 210° C.; andmaintaining a pressure in the reactor of at least approximately 2070kPa.

According to another embodiment, a method comprises: comminuting aninitial feedstock to form a primary feedstock that includes particleswhere the largest dimension of at least approximately 95% of theparticles in the primary feedstock is no more than 7 mm; oxidizing theprimary feedstock in a reactor, the primary feedstock being part of areaction mixture that also includes nitric acid and a secondaryoxidizing acid. The method may comprise feeding the primary feedstockinto the reactor at a feed rate that is approximately constant. Themethod may comprises combining an oxidizing acid with the initialfeedstock and/or the primary feedstock before the primary feedstockenters the reactor. The method may comprise combining effluent from thereactor with the initial feedstock and/or the primary feedstock beforethe primary feedstock enters the reactor. The initial feedstock mayinclude effluent from the reactor. The largest dimension of at leastapproximately 95% of the particles in the primary feedstock may be nomore than 4 mm. The largest dimension of at least approximately 95% ofthe particles in the primary feedstock may be no more than 2.5 mm. Thelargest dimension of at least approximately 95% of the particles in theprimary feedstock may be no more than 1.5 mm. The largest dimension ofat least approximately 95% of the particles in the primary feedstock maybe no more than 0.5 mm.

According to another embodiment, a method comprises: comminuting aninitial feedstock to form a primary feedstock that includes particleswhere the largest dimension of at least approximately 95% of theparticles in the primary feedstock is no more than 7 mm; oxidizing theprimary feedstock in a reactor, the primary feedstock being part of areaction mixture that also includes nitric acid and oxygen gas;supplying the oxygen gas to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid; andmaintaining the reaction mixture at a temperature that is no more thanapproximately 210° C. The method may comprise combining nitric acid withthe initial feedstock and/or the primary feedstock before the primaryfeedstock enters the reactor. The method may comprise combining effluentfrom the reactor with the initial feedstock and/or the primary feedstockbefore the primary feedstock enters the reactor. The initial feedstockmay include effluent from the reactor. The reaction mixture may includea secondary oxidizing acid. The largest dimension of at leastapproximately 95% of the particles in the primary feedstock may be nomore than 2.5 mm.

According to another embodiment, a method comprises: comminuting aninitial feedstock to form a primary feedstock that includes particleswhere the largest dimension of at least approximately 95% of theparticles in the primary feedstock is no more than 7 mm; oxidizing theprimary feedstock in a reactor, the primary feedstock being part of areaction mixture that also includes nitric acid; and maintaining apressure in the reactor of at least approximately 2070 kPa. The methodmay comprise combining nitric acid and a secondary oxidizing acid withthe initial feedstock and/or the primary feedstock before the primaryfeedstock enters the reactor. The method may comprise combining effluentfrom the reactor with the initial feedstock and/or the primary feedstockbefore the primary feedstock enters the reactor. The initial feedstockmay include effluent from the reactor. The largest dimension of at leastapproximately 95% of the particles in the primary feedstock may be nomore than 2.5 mm. The pressure in the reactor may be at least 2800 kPa.

According to another embodiment, a method comprises: comminuting aninitial feedstock to form a primary feedstock that includes particleswhere the largest dimension of at least approximately 95% of theparticles in the primary feedstock is no more than 7 mm; feeding theprimary feedstock into a reactor at an approximately constant feed rate;oxidizing the primary feedstock in the reactor, the primary feedstockbeing part of a reaction mixture that also includes nitric acid, asecondary oxidizing acid, and oxygen gas; supplying the oxygen gas tothe reaction mixture in an amount that is sufficient to regenerate atleast a majority of the nitric acid; maintaining the reaction mixture ata temperature that is no more than approximately 210° C.; andmaintaining a pressure in the reactor of at least approximately 2070kPa. The largest dimension of at least approximately 95% of theparticles in the primary feedstock may be no more than 2.5 mm. Theinitial feedstock may include effluent from the reactor. The maycomprise combining nitric acid and the secondary oxidizing acid with theinitial feedstock and/or the primary feedstock before the primaryfeedstock enters the reactor. The method may comprise: combiningeffluent from the reactor with the initial feedstock to form anintermediate feedstock; comminuting the intermediate feedstock to form acomminuted feedstock; and combining the comminuted feedstock, nitricacid, and the secondary oxidizing acid to form the primary feedstock.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor at a feed rate that is approximately constant; oxidizingthe feedstock in the reactor, the feedstock being part of a reactionmixture that also includes nitric acid and a secondary oxidizing acid;and maintaining a pressure in the reactor of at least approximately 2070kPa; wherein the feed rate is approximately constant even though thepressure in the reactor may vary from approximately 2070 kPa to 6,900kPa. The feedstock may be a slurry. The slurry may include nitric acidand/or the secondary oxidizing acid. The method may comprise a pluralityof feeding devices that are sequentially activated and refilled to feedthe feedstock into the reactor. The feedstock may include particleswhere the largest dimension of at least approximately 95% of theparticles in the feedstock is no more than 4 mm. The feedstock may befed into the reactor with a feeding device that is hydraulicly powered.The feedstock may be fed into the reactor with a feeding device that ispowered by a gearmotor.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor with a feeding device that is powered hydraulicly or by agearmotor; and oxidizing the feedstock in the reactor, the feedstockbeing part of a reaction mixture that also includes nitric acid and asecondary oxidizing acid. The method may comprise maintaining a pressurein the reactor of at least approximately 2070 kPa. The feedstock mayinclude particles where the largest dimension of at least approximately95% of the particles in the feedstock is no more than 4 mm. The methodmay comprise a plurality of the feeding devices that are sequentiallyactivated and refilled to feed the feedstock into the reactor. Thefeedstock may include effluent from the reactor and/or an oxidizingacid.

According to another embodiment, a method comprises: feeding a firstamount of a feedstock into a pressurized reactor with a feeding device;isolating the feeding device from the pressurized reactor; filling thefeeding device with a second amount of the feedstock; feeding the secondamount of the feedstock into the pressurized reactor with the feedingdevice; oxidizing the feedstock in the pressurized reactor, thefeedstock being part of a reaction mixture that also includes nitricacid and a secondary oxidizing acid; and maintaining a pressure in thereactor of at least approximately 2070 kPa. The method may comprise avalve that isolates the feeding device from the pressurized reactor. Thefirst amount of the feedstock and the second amount of the feedstock maybe fed into the pressurized reactor at a feed rate that is approximatelyconstant. Filling the feeding device with the second amount of thefeedstock may be done at a pressure that is greatly reduced from thepressure of the pressurized reactor. The pressure in the reactor may beat least 2800 kPa.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor at a feed rate that is approximately constant; oxidizingthe feedstock in the reactor, the feedstock being part of a reactionmixture that also includes nitric acid, a secondary oxidizing acid, andoxygen gas; supplying the oxygen gas to the reaction mixture in anamount that is sufficient to regenerate at least a majority of thenitric acid; maintaining the reaction mixture at a temperature that isno more than approximately 210° C.; and maintaining a pressure in thereactor of at least approximately 2070 kPa; wherein the feed rate isapproximately constant even though the pressure in the reactor may varyfrom approximately 2070 kPa to 6,900 kPa. The feedstock may includeparticles where the largest dimension of at least approximately 95% ofthe particles in the feedstock is no more than 4 mm. The method maycomprise a plurality of feeding devices that are sequentially activatedand refilled to feed the feedstock into the reactor. The feedstock mayinclude effluent from the reactor and/or an oxidizing acid.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor at a feed rate that fluctuates no more than approximately10% per hour; oxidizing the feedstock in a reactor, the feedstock beingpart of a reaction mixture that also includes nitric acid; andmaintaining a pressure in the reactor of at least approximately 2070kPa; wherein the feed rate fluctuates no more than approximately 10% perhour even though the pressure in the reactor may vary from approximately2070 kPa to 6,900 kPa.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor with a feeding device that is powered hydraulicly or by agearmotor; oxidizing the feedstock in the reactor, the feedstock beingpart of a reaction mixture that also includes nitric acid and oxygengas; supplying the oxygen gas to the reaction mixture in an amount thatis sufficient to regenerate at least a majority of the nitric acid; andmaintaining the reaction mixture at a temperature that is no more thanapproximately 210° C.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor with a feeding device that is powered hydraulicly or by agearmotor; oxidizing the feedstock in the reactor, the feedstock beingpart of a reaction mixture that also includes nitric acid; andmaintaining a pressure in the reactor of at least approximately 2070kPa.

According to another embodiment, a method comprises: feeding a feedstockinto a reactor with a feeding device that is powered hydraulicly or by agearmotor; oxidizing the feedstock in the reactor, the feedstock beingpart of a reaction mixture that also includes nitric acid, a secondaryoxidizing acid, and oxygen gas; supplying the oxygen gas to the reactionmixture in an amount that is sufficient to regenerate at least amajority of the nitric acid; maintaining the reaction mixture at atemperature that is no more than approximately 210° C.; and maintaininga pressure in the reactor of at least approximately 2070 kPa.

According to another embodiment, a method comprises: feeding a firstamount of a feedstock into a pressurized reactor with a feeding device;isolating the feeding device from the pressurized reactor; filling thefeeding device with a second amount of the feedstock; feeding the secondamount of the feedstock into the pressurized reactor with the feedingdevice; oxidizing the feedstock in the pressurized reactor, thefeedstock being part of a reaction mixture that also includes nitricacid; and maintaining a pressure in the pressurized reactor of at leastapproximately 2070 kPa; wherein the first amount of the feedstock andthe second amount of the feedstock are fed into the pressurized reactorat a feed rate that fluctuates no more than approximately 10% per hour;

According to another embodiment, a method comprises: feeding a firstamount of a feedstock into a pressurized reactor with a feeding device;isolating the feeding device from the pressurized reactor; filling thefeeding device with a second amount of the feedstock; feeding the secondamount of the feedstock into the pressurized reactor with the feedingdevice; oxidizing the feedstock in the pressurized reactor, thefeedstock being part of a reaction mixture that also includes nitricacid, a secondary oxidizing acid, and oxygen gas; supplying the oxygengas to the reaction mixture in an amount that is sufficient toregenerate at least a majority of the nitric acid; maintaining thereaction mixture at a temperature that is no more than approximately210° C.; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa; wherein the first amount of the feedstock andthe second amount of the feedstock are fed into the pressurized reactorat a feed rate that is approximately constant;

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and a secondary oxidizing acid; anddispersing gas from a headspace of the reactor into the reactionmixture. The method may comprise dispersing the gas from the headspaceinto the reaction mixture with an impeller that is hollow and causes gasfrom the headspace to flow through the impeller into the reactionmixture. The method may comprise dispersing the gas from the headspaceinto the reaction mixture with a gas entrainment impeller. The methodmay comprise supplying oxygen gas to the reactor and dispersing theoxygen gas from the headspace of the reactor into the reaction mixture.The method may comprise a baffle positioned in the reaction mixture toenhance the dispersion of the gas from the headspace into the reactionmixture. The method may comprise maintaining a pressure in the reactorof at least approximately 2070 kPa. The gas in the headspace may include2 to 60 volume percent oxygen gas.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and oxygen gas; supplying the oxygen gasto the reactor; dispersing the oxygen gas from a headspace of thereactor into the reaction mixture in a manner that is sufficient toregenerate at least a majority of the nitric acid; and maintaining thereaction mixture at a temperature that is no more than approximately210° C. The gas in the headspace may include 2 to 60 volume percentoxygen gas. The method may comprise dispersing the gas from theheadspace into the reaction mixture with an impeller that is hollow andcauses gas from the headspace to flow through the impeller into thereaction mixture. The method may comprise dispersing the gas from theheadspace into the reaction mixture with a gas entrainment impeller. Themethod may comprise maintaining a pressure in the reactor of at leastapproximately 2070 kPa.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and a secondary oxidizing acid; andmaintaining the concentration of dissolved and undissolved oxygen gas inthe gaseous portion of the reaction mixture within approximately 25% ofthe concentration of oxygen gas in a headspace of the reactor. Themethod may comprise maintaining the concentration of dissolved andundissolved oxygen gas in the gaseous portion of the reaction mixturewithin approximately 10% of the concentration of oxygen gas in theheadspace of the reactor. The method may comprise maintaining theconcentration of dissolved and undissolved oxygen gas in the gaseousportion of the reaction mixture within approximately 5% of theconcentration of oxygen gas in the headspace of the reactor. The methodmay comprise dispersing the oxygen gas from the headspace into thereaction mixture with a gas entrainment impeller. The headspace mayinclude 2 to 60 volume percent oxygen gas. The headspace may include 5to 45 volume percent oxygen gas.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid, a secondary oxidizing acid, and oxygengas; supplying oxygen gas to the reactor; dispersing oxygen gas from aheadspace of the reactor into the reaction mixture in a manner that issufficient to regenerate at least a majority of the nitric acid;maintaining the reaction mixture at a temperature that is no more thanapproximately 210° C.; and maintaining a pressure in the reactor of atleast approximately 2070 kPa. The method may comprise maintaining theconcentration of dissolved and undissolved oxygen gas in the gaseousportion of the reaction mixture within approximately 10% of theconcentration of oxygen gas in the headspace of the reactor. The methodmay comprise dispersing the oxygen gas from the headspace into thereaction mixture with an impeller that is hollow and causes the oxygengas from the headspace to flow through the impeller into the reactionmixture. The method may comprise dispersing the oxygen gas from theheadspace into the reaction mixture with a gas entrainment impeller.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid; dispersing gas from a headspace of thereactor into the reaction mixture; and maintaining a pressure in thereactor of at least approximately 2070 kPa.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and oxygen gas; supplying the oxygen gasto the reactor mixture in an amount that is sufficient to regenerate atleast a majority of the nitric acid; maintaining the concentration ofdissolved and undissolved oxygen gas in the gaseous portion of thereaction mixture within approximately 25% of the concentration of oxygengas in a headspace of the reactor; and maintaining the reaction mixtureat a temperature that is no more than approximately 210° C.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid; maintaining the concentration ofdissolved and undissolved oxygen gas in the gaseous portion of thereaction mixture within approximately 25% of the concentration of oxygengas in a headspace of the reactor; and maintaining a pressure in thereactor of at least approximately 2070 kPa.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid, a secondary oxidizing acid, and oxygengas; supplying the oxygen gas to the reaction mixture in an amount thatis sufficient to regenerate at least a majority of the nitric acid;maintaining the concentration of dissolved and undissolved oxygen gas inthe gaseous portion of the reaction mixture within approximately 25% ofthe concentration of oxygen gas in a headspace of the reactor;maintaining the reaction mixture at a temperature that is no more thanapproximately 210° C.; and maintaining a pressure in the reactor of atleast approximately 2070 kPa.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and a secondary oxidizing acid; supplyinggas to the reactor; and removing a reactor effluent from the reactor;wherein at least approximately 94 wt. % of the reaction mixture thatexits the reactor does so in the reactor effluent; and wherein at leastapproximately 94 wt. % of gas that exits the reactor does so in thereactor effluent. The method may comprise dispersing gas from aheadspace of the reactor into the reaction mixture. The method whereinat least approximately 98 wt. % of the reaction mixture that exits thereactor does so in the reactor effluent; and wherein at leastapproximately 98 wt. % of gas that exits the reactor does so in thereactor effluent. The method may comprise separating the gas from thereactor effluent. The method may comprise combining the feedstock withat least a portion of the reactor effluent. A headspace of the reactormay include 5 to 45 volume percent oxygen gas.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and oxygen gas; supplying gas to thereactor, the supplied gas including the oxygen gas; removing a reactoreffluent from the reactor; and maintaining the reaction mixture at atemperature that is no more than approximately 210° C.; wherein theoxygen gas is supplied to the reaction mixture in an amount that issufficient to regenerate at least a majority of the nitric acid; whereinat least approximately 94 wt. % of the reaction mixture that exits thereactor does so in the reactor effluent; and wherein at leastapproximately 94 wt. % of gas that exits the reactor does so in thereactor effluent. The method may comprise dispersing the oxygen gas froma headspace of the reactor into the reaction mixture. A headspace of thereactor may include 5 to 45 volume percent oxygen gas. The method maycomprise combining the feedstock with at least a portion of the reactoreffluent.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and a secondary oxidizing acid; supplyingoxygen gas to the reactor; removing a reactor effluent from the reactor;measuring the amount of oxygen gas in the reactor effluent; andadjusting the supply of oxygen gas to the reactor based on the amount ofoxygen gas measured in the reactor effluent. The method may comprisedispersing the oxygen gas from a headspace of the reactor into thereaction mixture. The method may comprise maintaining a pressure in thereactor of at least approximately 2070 kPa. The method may comprisesupplying inert gas to the reactor to maintain the pressure of at leastapproximately 2070 kPa. A headspace of the reactor may include 2 to 60volume percent oxygen gas. A headspace of the reactor may include 5 to45 volume percent oxygen gas.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid, a secondary oxidizing acid, and oxygengas; supplying gas to the reactor, the supplied gas including the oxygengas; removing a reactor effluent from the reactor; maintaining thereaction mixture at a temperature that is no more than approximately210° C.; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa; wherein the oxygen gas is supplied to thereaction mixture in an amount that is sufficient to regenerate at leasta majority of the nitric acid; wherein at least approximately 94 wt. %of the reaction mixture that exits the reactor does so in the reactoreffluent; and wherein at least approximately 94 wt. % of gas that exitsthe reactor does so in the reactor effluent. The method may comprisedispersing the oxygen gas from a headspace of the reactor into thereaction mixture. The method may comprise cooling the reactor effluent;and separating the gas from the reactor effluent. The reactor effluentmay be vigorously mixed at low pressure to separate the gas. A headspaceof the reactor may include 5 to 45 volume percent oxygen gas.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid; supplying gas to the reactor; removing areactor effluent from the reactor; and maintaining a pressure in thereactor of at least approximately 2070 kPa; wherein at leastapproximately 94 wt. % of the reaction mixture that exits the reactordoes so in the reactor effluent; and wherein at least approximately 94wt. % of gas that exits the reactor does so in the reactor effluent.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and oxygen gas; supplying the oxygen gasto the reactor in an amount that is sufficient to regenerate at least amajority of the nitric acid; removing a reactor effluent from thereactor; measuring the amount of oxygen gas in the reactor effluent;adjusting the supply of oxygen gas to the reactor based on the amount ofoxygen gas measured in the reactor effluent; and maintaining thereaction mixture at a temperature that is no more than approximately210° C.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid; supplying oxygen gas to the reactor;removing a reactor effluent from the reactor; measuring the amount ofoxygen gas in the reactor effluent; adjusting the supply of oxygen gasto the reactor based on the amount of oxygen gas measured in the reactoreffluent; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa.

According to another embodiment, a method comprises: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid, a secondary oxidizing acid, and oxygengas; supplying oxygen gas to the reactor; removing a reactor effluentfrom the reactor; measuring the amount of oxygen gas in the reactoreffluent; adjusting the supply of oxygen gas to the reactor based on theamount of oxygen gas measured in the reactor effluent; maintaining thereaction mixture at a temperature that is no more than approximately210° C.; and maintaining a pressure in the reactor of at leastapproximately 2070 kPa; wherein the oxygen gas is supplied to thereaction mixture in an amount that is sufficient to regenerate at leasta majority of the nitric acid.

The terms recited in the claims should be given their ordinary andcustomary meaning as determined by reference to relevant entries (e.g.,definition of “plane” as a carpenter's tool would not be relevant to theuse of the term “plane” when used to refer to an airplane, etc.) indictionaries (e.g., widely used general reference dictionaries and/orrelevant technical dictionaries), commonly understood meanings by thosein the art, etc., with the understanding that the broadest meaningimparted by any one or combination of these sources should be given tothe claim terms (e.g., two or more relevant dictionary entries should becombined to provide the broadest meaning of the combination of entries,etc.) subject only to the following exceptions: (a) if a term is usedherein in a manner more expansive than its ordinary and customarymeaning, the term should be given its ordinary and customary meaningplus the additional expansive meaning, or (b) if a term has beenexplicitly defined to have a different meaning by reciting the termfollowed by the phrase “as used herein shall mean” or similar language(e.g., “herein this term means,” “as defined herein,” “for the purposesof this disclosure [the term] shall mean,” etc.). References to specificexamples, use of “i.e.,” use of the word “invention,” etc., are notmeant to invoke exception (b) or otherwise restrict the scope of therecited claim terms. Other than situations where exception (b) applies,nothing contained herein should be considered a disclaimer or disavowalof claim scope. The subject matter recited in the claims is notcoextensive with and should not be interpreted to be coextensive withany particular embodiment, feature, or combination of features shownherein. This is true even if only a single embodiment of the particularfeature or combination of features is illustrated and described herein.Thus, the appended claims should be read to be given their broadestinterpretation in view of the prior art and the ordinary meaning of theclaim terms.

As used herein, spatial or directional terms, such as “left,” “right,”“front,” “back,” and the like, relate to the subject matter as it isshown in the drawing FIGS. However, it is to be understood that thesubject matter described herein may assume various alternativeorientations and, accordingly, such terms are not to be considered aslimiting. Furthermore, as used herein (i.e., in the claims and thespecification), articles such as “the,” “a,” and “an” can connote thesingular or plural. Also, as used herein, the word “or” when usedwithout a preceding “either” (or other similar language indicating that“or” is unequivocally meant to be exclusive—e.g., only one of x or y,etc.) shall be interpreted to be inclusive (e.g., “x or y” means one orboth x or y). Likewise, as used herein, the term “and/or” shall also beinterpreted to be inclusive (e.g., “x and/or y” means one or both x ory). In situations where “and/or” or “or” are used as a conjunction for agroup of three or more items, the group should be interpreted to includeone item alone, all of the items together, or any combination or numberof the items. Moreover, terms used in the specification and claims suchas have, having, include, and including should be construed to besynonymous with the terms comprise and comprising.

Unless otherwise indicated, all numbers or expressions, such as thoseexpressing dimensions, physical characteristics, etc. used in thespecification (other than the claims) are understood as modified in allinstances by the term “approximately.” At the very least, and not as anattempt to limit the application of the doctrine of equivalents to theclaims, each numerical parameter recited in the specification or claimswhich is modified by the term “approximately” should at least beconstrued in light of the number of recited significant digits and byapplying ordinary rounding techniques. Moreover, all ranges disclosedherein are to be understood to encompass and provide support for claimsthat recite any and all subranges or any and all individual valuessubsumed therein. For example, a stated range of 1 to 10 should beconsidered to include and provide support for claims that recite any andall subranges or individual values that are between and/or inclusive ofthe minimum value of 1 and the maximum value of 10; that is, allsubranges beginning with a minimum value of 1 or more and ending with amaximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and soforth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

What is claimed is:
 1. A method comprising: comminuting an initialfeedstock to form a primary feedstock that includes particles where thelargest dimension of at least approximately 95% of the particles in theprimary feedstock is no more than 7 mm; and oxidizing the primaryfeedstock in a reactor, the primary feedstock being part of a reactionmixture that also includes nitric acid and a secondary oxidizing acid;wherein the reaction mixture, excluding solids, includes no more than 5wt % of the secondary oxidizing acid.
 2. The method of claim 1comprising feeding the primary feedstock into the reactor at a feed ratethat is approximately constant.
 3. The method of claim 1 comprisingcombining an oxidizing acid with the initial feedstock and/or theprimary feedstock before the primary feedstock enters the reactor. 4.The method of claim 1 comprising combining effluent from the reactorwith the initial feedstock and/or the primary feedstock before theprimary feedstock enters the reactor.
 5. The method of claim 1 whereinthe initial feedstock includes effluent from the reactor.
 6. The methodof claim 1 wherein the largest dimension of at least approximately 95%of the particles in the primary feedstock is no more than 4 mm.
 7. Themethod of claim 1 wherein the largest dimension of at leastapproximately 95% of the particles in the primary feedstock is no morethan 2.5 mm.
 8. The method of claim 1 wherein the largest dimension ofat least approximately 95% of the particles in the primary feedstock isno more than 1.5 mm.
 9. The method of claim 1 wherein the largestdimension of at least approximately 95% of the particles in the primaryfeedstock is no more than 0.5 mm.
 10. A method comprising: oxidizing afeedstock in a reactor, the feedstock being part of a reaction mixturethat also includes nitric acid and a secondary oxidizing acid; whereinthe reaction mixture, excluding solids, includes no more than 5 wt % ofthe secondary oxidizing acid.
 11. The method of claim 10 comprisingcombining nitric acid with the feedstock before the feedstock enters thereactor.
 12. The method of claim 10 comprising combining effluent fromthe reactor with the feedstock before the feedstock enters the reactor.13. The method of claim 10 wherein the feedstock includes effluent fromthe reactor.
 14. The method of claim 10 comprising maintaining thereaction mixture at a temperature that is no more than approximately210° C.
 15. The method of claim 10 wherein the feedstock is a primaryfeedstock, the method comprising comminuting an initial feedstock toform the primary feedstock, wherein the largest dimension of at leastapproximately 95% of the particles in the primary feedstock is no morethan 7 mm.
 16. A method comprising: oxidizing a feedstock in a reactor,the feedstock being part of a reaction mixture that also includes nitricacid and a secondary oxidizing acid; wherein the reaction mixture,excluding solids, includes no more than approximately 3 wt % of thesecondary oxidizing acid.
 17. The method of claim 16 comprisingcombining nitric acid and the secondary oxidizing acid with thefeedstock before the feedstock enters the reactor.
 18. The method ofclaim 16 comprising combining effluent from the reactor with thefeedstock before the feedstock enters the reactor.
 19. The method ofclaim 16 wherein the feedstock includes effluent from the reactor. 20.The method of claim 16 comprising maintaining a pressure in the reactorof at least approximately 2070 kPa.
 21. The method of claim 20 whereinthe pressure in the reactor is at least 2800 kPa.
 22. A methodcomprising: oxidizing a feedstock in the reactor, the feedstock beingpart of a reaction mixture that also includes nitric acid, a secondaryoxidizing acid, and oxygen gas; dispersing oxygen gas from a headspaceof the reactor into the reaction mixture; maintaining the reactionmixture at a temperature that is no more than approximately 210° C.; andmaintaining a pressure in the reactor of at least approximately 2070kPa; wherein the reaction mixture, excluding solids, includes no morethan 5 wt % of the secondary oxidizing acid.
 23. The method of claim 22wherein the feedstock is a primary feedstock, the method comprisingcomminuting an initial feedstock to form the primary feedstock, whereinthe largest dimension of at least approximately 95% of the particles inthe primary feedstock is no more than 7 mm.
 24. The method of claim 22wherein the feedstock includes effluent from the reactor.
 25. The methodof claim 22 comprising combining nitric acid and the secondary oxidizingacid with the feedstock before the feedstock enters the reactor.
 26. Themethod of claim 22 wherein the feedstock is a primary feedstock, themethod comprising: combining effluent from the reactor with an initialfeedstock to form an intermediate feedstock; comminuting theintermediate feedstock to form a comminuted feedstock; and combining thecomminuted feedstock, nitric acid, and the secondary oxidizing acid toform the primary feedstock.
 27. The method of claim 1 wherein thesecondary oxidizing acid includes sulfuric acid.
 28. The method of claim1 wherein the reaction mixture, excluding solids, includes no more thanapproximately 3 wt % of the secondary oxidizing acid.
 29. The method ofclaim 28 wherein the secondary oxidizing acid includes sulfuric acid.30. The method of claim 1 wherein the reaction mixture, excludingsolids, includes no more than approximately 15 wt % nitric acid.
 31. Themethod of claim 10 comprising maintaining a pressure in the reactor ofat least approximately 2070 kPa.
 32. The method of claim 10 comprisingdispersing oxygen gas from a headspace of the reactor into the reactionmixture.
 33. The method of claim 32 wherein the headspace includes 2 to60 volume percent oxygen gas.
 34. The method of claim 10 wherein thesecondary oxidizing acid includes sulfuric acid.
 35. The method of claim10 wherein the reaction mixture, excluding solids, includes no more thanapproximately 15 wt % nitric acid.
 36. The method of claim 16 whereinthe feedstock is a primary feedstock, the method comprising comminutingan initial feedstock to form the primary feedstock, wherein the largestdimension of at least approximately 95% of the particles in the primaryfeedstock is no more than 7 mm.
 37. The method of claim 16 wherein thesecondary oxidizing acid includes sulfuric acid.
 38. The method of claim16 comprising dispersing oxygen gas from a headspace of the reactor intothe reaction mixture.
 39. The method of claim 38 wherein the headspaceincludes 2 to 60 volume percent oxygen gas.
 40. The method of claim 16wherein the reaction mixture, excluding solids, includes no more thanapproximately 15 wt % nitric acid.
 41. The method of claim 16 comprisingmaintaining the reaction mixture at a temperature that is no more thanapproximately 210° C.
 42. The method of claim 22 wherein the secondaryoxidizing acid includes sulfuric acid.
 43. The method of claim 22wherein the reaction mixture, excluding solids, includes no more thanapproximately 3 wt % of the secondary oxidizing acid.
 44. The method ofclaim 43 wherein the secondary oxidizing acid includes sulfuric acid.45. The method of claim 22 wherein the reaction mixture, excludingsolids, includes no more than approximately 15 wt % nitric acid.